Method and apparatus for purifying air from biological agents and volatile organic compounds

ABSTRACT

A method for improving indoor air quality in a room, comprising drawing air from the room and guiding the air into a gas/liquid contactor charged with aqueous alkali hydroxide/H 2 O 2  solution, passing the air through a perforated membrane installed in the gas/liquid contactor below the surface level of the aqueous alkali hydroxide/H 2 O 2  solution, such that bubbles produced travel through said solution, and getting treated air with improved quality from said gas/liquid contactor, said treated air is characterized by having: reduced carbon dioxide levels; and/or reduced VOC levels; and/or reduced microbiological load. An air purifier to carry out the method is also provided.

FIELD OF THE INVENTION

The invention generally relates to systems and methods for airtreatment. More specifically, the invention relates to a method forpurifying air from chemical and biological pollutants, such as VolatileOrganic Compounds (VOCs), formaldehyde, viruses, bacteria, etc., and toa domestic system for air purification, achieving reduction of CO₂levels and biological load.

BACKGROUND OF THE INVENTION

Heating, ventilation and air conditioning (HVAC) systems used in homesand offices facilitate the accumulation of air pollutants withinair-regulated closed spaces. A central HVAC system that operates in anoffice building accumulates outdoor air, regulates its temperature andmoisture, and circulates the regulated air within spaces of thebuilding. However, the air which is brought from the outdoor to thesystem is in many cases polluted, resulting in a conveyance ofmicro-particles of, for example, dust, smoke, smog, chemicals, etc. intothe closed space, and additional micro-particles are added from withinthe spaces themselves. The situation is similarly problematic in theair-conditioning of small homes, where the indoor air is circulated in aclosed-loop, without even adding outdoor refreshing air into the loop.Both cases (i.e., of office-buildings and small homes) result in theaccumulation of solid particles and gases, such as dust, smoke, smog,and bio-hazards such as viruses and bacteria, within the air-regulatedspaces. These micro-pollutants impair health and productivity.

A variety of domestic air purifiers (hereinafter also referred to as“home-purifiers” or “room purifiers” that are used in individual roomsat homes, offices, hospitals, medical clinics, waiting rooms, etc.) thatare supplementary to existing HVAC systems have been developed to reducethe accumulation of polluting particles in closed spaces. These arestand-alone devices that typically include a quiet blower and a set ofone or more fine filters. These air purifiers are designed to circulatethe room's air through the set of fine filters, thereby capturingparticles in sizes ranging from 1 μm to 10 μm and larger. 1 μm particlesgenerally originate from smoke and smog, 2.5 μm particles originate frommotor-vehicle exhausts and wood-burning fires, and 10 μm and largerparticles originate from general dust. While capturing up to 99% ofthose micro-sized particles, these traditional air purifiers are usuallynot effective against a multitude of chemical and biologicalcontaminants, i.e., reduction of carbon dioxide indoor levels, alongsideVolatile Organic Compounds (VOCs), (e.g., formaldehyde), allergens,bacteria, viruses, etc.

There exists a need to provide a domestic air purifier having thecapability of removing airborne chemical and biological pollutants.

Incorporation of chemistry into air purifiers to improve the quality ofindoor air by reduction of biological load is described in JP2003-161482 (electrochemically generated H₂O₂ solution), JP 2001-062239and CN 2675130 (the treated air is passed through chemical solutionsarranged successively, including alkali hydroxide and sodium peroxide).

An aqueous alkali hydroxide/H₂O₂ solution (i.e., an alkali hydroxidesolution to which H₂O₂ is added, hereinafter also named “MOH/H₂O₂reagent”; M stands for the alkali metal, e.g., sodium, potassium or amixture thereof) has been previously reported as a generator of thesuperoxide radical anion (O₂—.). In a series of publications (WO2013/093903; Stoin, U. et al. ChemPhysChem, 2013, 14, 4158 and WO2015/170317), it was shown that the aqueous MOH/H₂O₂ reagent is apowerful oxidizer that could be used to serve several useful purposes:

absorbing carbon dioxide from flue gases;

destroying bulk carbon tetrachloride and other chlorinated methane andethane compounds; and

remediating soil from diesel oil and crude oil contaminants.

In co-assigned WO 2018/002710, the focus was shifted to air treatment,proposing using the aqueous MOH/H₂O₂ reagent for removing target gasesfrom the air, mainly carbon monoxide arising in case of fire. Othertarget gases which the MOH/H₂O₂ reagent could neutralize are listed onpage 15 of WO 2018/002710. The system described in WO 2018/002710includes an inlet that receives a flow of contaminated air from thetreated space and a reaction chamber that contains an aqueous solutionsuch that an amount of one or more target gas species contained within aplurality of bubbles are reduced through reaction with the solution. Thetreated air that flows out of the solution is then returned into thetreated space. WO 2018/002710 demonstrates the efficiency of thereaction chamber in converting toxic gases (such as carbon monoxide,carbon dioxide, NOx, etc.) to harmless chemical substances, e.g.,oxygen, therefore facilitating breathing, particularly in the case ofhighly contaminated air during a fire. However, the state of a home oroffice room in a normal condition is substantially different from thestate of the fire-polluted air treatment as demonstrated by WO2018/002710, as the concentration rate of contaminants in the case offire is several orders higher compared to a room in normal conditions.

In another aspect, a conventional domestic air-purifier is a stationaryunit, requiring the positioning of a dedicated unit in each room to betreated, no matter whether the rate of contaminants in the room in agiven time is above a harmful threshold or not. This configurationresults in waste of resources or compromise of air-quality in roomswhere a home-purifier is not positioned.

It is an object of the present invention to provide a novelhome-purifier for reducing bio-hazards.

Another object of the present invention is to provide a home-purifierthat reduces hazardous or harmful gases and bio-hazards.

Another object of the invention is to provide said novel home-purifierin a compact size and quietness of operation.

Still another object the invention is to provide a single home airpurifier capable of treating a plurality of rooms within an office orhome.

Still, another object of the present invention is to provide a compactreactor within said compact and quiet home air purifier for reducingbio-hazards and hazardous or harmful gases.

It is still another object of the present invention to integrate thehome air purifier of the present invention with a traditional home airpurifier.

Other objects and advantages of the invention become apparent as thedescription proceeds.

SUMMARY OF THE INVENTION

The present invention is specifically aimed at addressing the need tomaintain good indoor air quality. Contaminants found in indoor air inbuildings and structures are classified into two groups: chemicalcontaminants and biological contaminants.

A major chemical contaminant is formaldehyde, a colorless,pungent-smelling gas which is considered by the United StatesEnvironmental Protection Agency to be an important hazardous airpollutant, arising from glues and foams used in furniture, some textiles(e.g., carpets), and from combustion processes such as cooking andsmoking. The major biological contaminants are bacteria, fungi, andviruses.

Experimental work conducted in support of this invention indicates thatthe MOH/H₂O₂ reagent can reduce VOC levels (e.g., formaldehyde) inindoor air. The MOH/H₂O₂ reagent has demonstrated high, steadyconversion rates of gaseous formaldehyde into harmless by-products overa long test period, challenging characteristic formaldehyde levels (fewtenths of a milligram per cubic meter, ˜0.2 mg/m³). Likewise, low carbondioxide concentrations in indoor air could also be effectively targetedby the MOH/H₂O₂ reagent, leading to essentially complete elimination ofcarbon dioxide with a potential benefit of oxygen generation (O₂ isby-product of CO₂ oxidation by superoxide).

Results reported below also indicate that the MOH/H₂O₂ reagent possessesair-sanitizing action. That is, it acts on airborne microorganism. TheMOH/H₂O₂ reagent may therefore be used to control microbiological loadin indoor air, specifically by eliminating bacteria. Hydrogen peroxideis known to act on bacteria, but the antibacterial effect of theMOH/H₂O₂ reagent is surprising, bearing in mind that hydrogen peroxidedecomposes instantly in an alkaline environment. Experimental workconducted in support to this invention shows that when air stream thatwas loaded with a bioaerosol (produced from bacteria (K. rhizophila) wastreated with the MOH/H₂O₂ reagent, high log reduction of bacterial loadwas measured versus control. The MOH/H₂O₂ reagent is also effective incombatting viruses: in the experimental model described below, a removalrate of more than 99.9% was measured (the tested virus was a coronavirus, e.g., human coronavirus such as OC43).

As shown below in reference to the drawings, several reactorconfigurations could be used to achieve an efficient contact between theincoming indoor air stream and the aqueous MOH/H₂O₂ reagent, mainlybased on the creation of air bubbles that are forced to travel throughthe bulk reagent.

One major aspect of the invention is therefore a method for improvingindoor air quality in a room, comprising drawing air from the room andguiding the air to a gas/liquid contactor charged with aqueous alkalihydroxide/H₂O₂ solution, passing the air through a perforated membraneinstalled in the gas/liquid contactor below the surface level of theaqueous alkali hydroxide/H₂O₂ solution, such that bubbles producedtravel through said solution, and getting treated air with improvedquality from said gas/liquid contactor, said treated air ischaracterized by having:

reduced carbon dioxide levels (from 1000-200,000 ppm, e.g., from1000-10,000, down to less than 1000 ppm, e.g., down to 400-700 ppm);and/or

reduced VOC (e.g., formaldehyde) levels; and/or

reduced microbiological load (e.g., at least 1-log reduction ofbacterial load and/or viral load, e.g., at least 2-log reduction).Another benefit gained is oxygen enrichment in indoor environment, up to233.

The term “perforated membrane”, as used herein, relates to a perforatedelement allowing passage of air therethrough, to disperse the air streamand create bubbles within a solution. It can have a flat geometry,(e.g., membrane 836 as shown in FIG. 16 l ) or a tubular geometry (e.g.,membrane 936 as shown in FIG. 18 a , where the membrane has a perforatedspiral tubing configuration). The terms “reactor” and “gas/liquidcontactor” are used herein interchangeably.

The invention also relates to an air purifier for eliminating chemicaland biological pollutants from a room, which comprises: (a) an inlet airchannel; (b) one or more air sucking components configured to direct airfrom the room into said inlet channel, and to direct the air via saidair channel into a perforated membrane mounted in a chemical andbiological pollutants-elimination reactor; and (c) an outlet air channelconfigured to receive treated air from the reactor; (d) wherein thereactor comprises: (d.1) a reservoir configured to contain a purifyingaqueous alkali hydroxide/H₂O₂ solution; wherein during the purifier'soperation, said perforated membrane is positioned below a surface levelof the solution such that air passing through the perforated membrane isconverted into bubbles that travel through the solution and towards saidoutlet channel; and wherein the air purifier further comprises aremovable storage unit positioned above the reactor, said removablestorage unit is configured to contain and supply alkali hydroxide,hydrogen peroxide, and optionally water to said reactor.

In an embodiment of the invention, said inlet air channel conveys air ina downwards direction, the inlet air channel passes through an openingin said perforated membrane towards an air compartment located below theperforated membrane.

In an embodiment of the invention, a bottom outlet of said inlet airchannel is sealed against a top surface of the perforated membrane,thereby allowing passage of air from the inlet air channel only throughthe perforations of the membrane towards a section of the reservoirbelow the membrane, and wherein the diameter of said membrane is smallerthan the diameter of the reservoir of alkali hydroxide/H₂O₂ solution.

In an embodiment of the invention, each perforation at the membrane hasa diameter in the range of 40 μm and 1200 μm.

In an embodiment of the invention, each of the perforations has top andbottom openings, respectively, at top and bottom surfaces of theperforated membrane, the diameter of said top opening is larger than adiameter of said bottom opening.

In an embodiment of the invention, each of the perforations is dividedinto two sections in cross-section, a lower section having a cylindricalshape, and an upper section having a frustoconical shape.

In an embodiment of the invention, a bottom outlet of said inlet airchannel is configured to lead contaminated air to a perforated membrane,said perforated membrane having a spiral tubing configuration andpositioned at a lower portion of said purifying solution's reservoir.

In an embodiment of the invention, each said perforations is positionedat a lower portion of the tubing in cross section, thereby directing airoutlet through the perforation downwards.

In an embodiment of the invention, each of said perforations ispositioned at least 30° lower than the tubing horizontal diameter incross-section. In this embodiment of the invention, each of saidperforations has a diameter in the range of between 40 μm and 1200 μm.

In an embodiment of the invention, a distance between each twoperforations is in the range of 2-50 of the perforation's diameter.

In an embodiment of the invention, said storage unit comprises an alkalihydroxide container, a H₂O₂ container, and optionally a water container.

In an embodiment of the invention, the air purifier has an essentiallycylindrical shape, wherein said alkali hydroxide container, said H₂O₂container, and said water container are arranged concentrically withinthe storage unit.

In an embodiment of the invention, the alkali hydroxide container isconfigured to contain alkali hydroxide tablets in a releasablearrangement.

In an embodiment of the invention, the alkali hydroxide containercomprises a plurality of columns, each column is configured to storealkali hydroxide tablets.

In an embodiment of the invention, the alkali hydroxide container isconfigured to angularly revolve, thereby to position a single columnabove an opening to a passage leading to said solution reservoir,thereby to allow a periodical feeding of the solution by hydroxidetablets.

In an embodiment of the invention, the air purifier has a blower and aHEPA filter fitted in the inlet channel upstream to the reactor.

In an embodiment of the invention, the air purifier is integrated with adomestic room purifier having a HEPA filter, wherein the inlet airchannel is a branch from an inlet air channel of the domestic roompurifier diverging downstream to the HEPA filter, and wherein the outletchannel joins an outlet channel of the domestic room purifier.

In an embodiment of the invention, the air purifier further comprising asensor for measuring a concentration of CO₂ at the room-air, and whereina schedule and a period of operation of the device is based on CO₂measurements by said sensor.

The invention also relates to a home air purifying system, comprises:(a) a plurality of air-quality sensors, each sensor being positioned atanother room of the home; (b) a docking station which is configured to:(b.1) host a mobile, air purifier; (b.2) receive air qualitymeasurements from all said plurality of sensors, and determine when alevel of contamination at a room exceeds a predefined contaminationthreshold; and (b.3) communicate with said mobile air purifier, and atleast send to it an indication of a room in which a contamination abovesaid predefined contamination threshold has been detected; and (c) saidmobile air purifier, which is configured to: (c.1) communicate with saiddocking station, and at least receive from it an indication of the roomin which the contamination above said predefined contamination thresholdhas been detected; (c.2) upon receipt of said indication, navigate tothe contaminated room, operate there to purify the room, and uponcompletion, return to the docking station.

In an embodiment of the invention, said contamination comprises one ormore chemical and biological contaminants.

In an embodiment of the invention, said mobile air purifier comprises:(a) an inlet air channel; (b) one or more air sucking componentsconfigured to suck air from the room into said inlet channel, and todirect the air via said air channel into a perforated membrane mountedat a bio-hazards elimination reactor; and (c) an outlet air channelconfigured to receive treated air from the reactor, and to return thetreated air into the room; wherein the bio-hazards elimination reactorcomprising: (d) a reservoir configured to contain a purifying aqueousalkali hydroxide/H₂O₂ solution; wherein during the purifier operationsaid perforated membrane is positioned below a surface level of thesolution such that air passing through the perforated membrane isconverted into bubbles that travel through the solution and towards saidoutlet channel; and wherein the air purifier further comprising aremovable storage unit positioned above the reactor, said removablestorage unit is configured to contain and supply alkali hydroxide,hydrogen peroxide, and water to said reactor.

For example, an aqueous alkali hydroxide/H₂O₂ solution is charged to thegas/liquid contactor either by feeding alkali hydroxide solutionprepared beforehand, or by dissolving solid alkali hydroxide (e.g., in atablet or granular form) in water supplied separately to the gas/liquidcontactor, with continuous or periodic addition of hydrogen peroxidesolution to the alkali hydroxide solution.

For example, air bubbles (created by forcing the incoming air stream toflow across a membrane as described in detail below) are caused totravel through the alkali hydroxide solution (e.g., NaOH or KOH, ortheir mixture), to which H₂O₂ stream is periodically or continuouslyadded (for example, by injection beneath the level of the alkalihydroxide solution, in close proximity to the perforated membrane, i.e.,in the vicinity of the perforations). Concentration of the alkalihydroxide solution varies from 5% to 48%-50% by weight, e.g., from 10 to48%-50% by weight. The concentration of the hydrogen peroxide solutionadded to the alkali hydroxide solution is from 3%, 4- or 5% up to 35% byweight, e.g., from 10 to 30% by weight. Acceptable addition rate of theH₂O₂ stream may vary from 0.01 ml/min to 10 ml/min, e.g. up to 2, 3 or 4ml/min. The volumetric ratio between the solutions in the range of 2:1to 10:1 in favor of the alkali hydroxide solution. The proportion can beadjusted according to the profile of pollutants. As mentioned above,chemical pollutants targeted by the invention include carbon dioxide andVOC; biological pollutants include bacteria and viruses such as coronavirus, e.g., human coronavirus such as OC43.

A perforated membrane with flat (planar) geometry is preferablyhorizontally mounted in the vertically positioned air-purifier. Suitableperforated membranes are 1-10 mm thick, made of chemically inertmaterials (stainless steel, plastic, etc.), and have 40-1200 μm diameterholes, which are generally evenly distributed over the membrane. Thediameter of a hole may be constant, i.e., it does not vary within themembrane thickness, such that the two opposing sides of a passage (ahole) are equal in diameter. One design of the perforated membraneinvolves variation of the diameter of the perforations (holes) throughwhich the air flows to cross the membrane. Preferably, the air is passedthrough the membrane via perforations whose diameter increases acrossthe membrane thickness (in operation, the diameter increases from thebottom surface to top surface of the membrane); the perforations arepassages consisting of a cylindrical section (with diameter(D_(cylinder)) in the range from, e.g., 0.08 mm to 1 mm) joining aninverted frustoconical section facing the solution (the diameter of thesmall base of the frustoconical equals D_(cylinder); the diameter of thelarge base of the frustoconical section, facing the solution, is 1.3 to2.0 times larger than D_(cylinder), with separation between theperforations (passages) being at least 3 times larger thanD_(cylinder)). Alternatively, the passage is shaped as a frustrum of acone having a small base and a large base; the air passes through themembrane by entering through the small base and exiting through thelarge base facing the solution. The benefits received from this geometryare explained below.

With the aid of HEPA filter (high-efficiency particulate filter) addedand a blower, the device described above can function as a stand-aloneair purifier that reduces the chemical and microbial load of an indoorenvironment. Alternatively, it may be coupled to conventional airpurifiers or HVAC systems. As pointed out above, a conventional airpurifier (equipped with a static filter) or HVAC system could benefitfrom an auxiliary unit integrated thereinto to treat a secondary airstream that has been diverted from the main airflow, with the aid of theMOH/H₂O₂ reagent. The chemically and/or biologically decontaminated airthus generated (e.g., with reduced formaldehyde and/or CO₂ levels and/orreduced microbiological load) is guided to join the main airflowreleased from the conventional air purifier, as illustrated below inFIG. 5 . In another embodiment, the air-purifier of the invention mayoperate independently while including an internal HEPA filter, asdescribed below in the embodiment of FIGS. 16 a -16 p.

Accordingly, the air drawn into the gas/liquid contactor (where theMOH/H₂O₂ reagent is placed) is a filtered air stream resulting frompassing indoor air through a filter that captures particles.

A specific aspect of the invention is a method for improving indoor airquality, comprising the steps of:

drawing indoor air and passing same, at a first flow rate, across afilter to capture airborne particles and produce a main filtered airstream;

diverting a portion of the main filtered air stream to generate asecondary filtered air stream flowing at a second flow rate, forcingsaid secondary filtered air stream into a gas/liquid contactor chargedwith the MOH/H₂O₂ reagent, where the filtered air, in the form ofbubbles, is contacted with the MOH/H₂O₂ reagent;

withdrawing filtered and decontaminated air stream from said gas/liquidcontactor; and

joining said filtered and decontaminated air stream with the mainfiltered air stream.

Characteristic flow rates for the main filtered air stream and secondaryfiltered air stream may be from 500 to 8000 L/min and 80 to 1,000 L/min,respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 schematically illustrates a general structure of a traditional(prior art) home air purifier;

FIG. 2 schematically illustrates a general structure of an air treatmentunit as disclosed by WO 2018/002710;

FIG. 3 a shows a stand-alone home air purifier according to anembodiment of the present invention;

FIGS. 3 b and 3 c are two side-views of the home air purifier presentedin FIG. 3 a;

FIG. 4 illustrates a reactor structure according to a second embodimentof the invention;

FIG. 5 illustrates an integration between a traditional filter-basedhome air purifier and the air purifier of the invention;

FIG. 6 shows a structure of a mobile home air purifying system,according to an embodiment of the invention;

FIG. 7 shows an exemplary configuration of the system of FIG. 6 for theelimination of bio-hazards; and

FIG. 8 shows an exemplary docking station and a mobile purifieraccording to an embodiment of the invention.

FIG. 9 shows an experimental set-up used for testing removal offormaldehyde from the air, with the aid of NaOH/H₂O₂ reagent.

FIG. 10 shows formaldehyde concentration versus time plot.

FIG. 11 shows formaldehyde concentration versus time plot, measured inthe incoming (contaminated) and outgoing (treated) air streams.

FIG. 12 shows an experimental set-up used for testing removal of CO₂from the air with the aid of NaOH/H₂O₂ reagent.

FIG. 13 shows CO₂ concentration versus time plot, measured in theincoming (contaminated) and outgoing (treated) air streams.

FIG. 14 shows oxygen concentration versus time plot, measured in theincoming (contaminated) and outgoing (treated) air streams.

FIG. 15 shows an experimental set-up used for testing the removal ofbacteria from the air with NaOH/H₂O₂ reagent aid.

FIGS. 16 a-16 p illustrate a structure of a home-purifier according to athird embodiment of the invention. FIGS. 16 b and 16 c are schematicdiagrams. FIGS. 16 h, 16 i, and 16 j provide partial illustrations,respectively, of the home-purifier. FIGS. 16 e, 16 f, and 16 g providecross-sectional views of the home-purifier. FIGS. 16 k-16 n describe thestructure of the perforated membrane of the home-purifier, and FIGS. 16o and 16 p describe the improved effect of bubble creation obtained bythe perforated membrane of the invention, compared to a conventionalperforated membrane;

FIG. 17 shows an experimental set-up used for testing the removal ofbacteria from the air with NaOH/H2O2 reagent aid;

FIGS. 18 a-18 d describe a fourth embodiment of the home purifier; and

FIG. 19 is a bar diagram showing the performance of different types ofperforated membranes.

FIGS. 20-21 show another design of an air purifier of the invention,based on a battery consisting of a solid CO₂ sorbent and the MOH/H₂O₂reactor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a general structure of a traditional(prior art) home (domestic) air purifier 100. The purifier generallyincludes a stand (base) S, an air inlet 110, an air blower B, a set ofone or more filters F (typically High-efficiency particulate HEPA-typefilters), a control unit C, a control panel P, one or more sensors 112,and an air outlet 114. In operation, blower B (the term “blower” is alsoreferred to herein as “air sucking component”) continuously sucks viainlet 110 contaminated air 120 from the room and directs the air througha set of one or more filters F. Filters F capture contaminatingparticles suspended in the air, forming a purified airflow 122, which isreturned into the room via outlet 114. Typically, home air purifier 100also includes at least one sensor 112 for sensing the level ofcontaminants in the air in the room, and the level of air quality isindicated on a display within control panel P. The control panel Ptypically includes said display and controls for selecting a desiredoperational mode of the device and a level of a necessary purification(for example, in terms of airborne particle concentration). Home airpurifier 100 is capable of efficiently removing only solid particles ofdimensions typically as small as 0.3 μm, as its filtering capabilitysolely depends on passive filters F. This type of home air purifier,however, is incapable of removing neither biological agents (such asviruses and small bacteria, etc.) nor hazardous gases.

FIG. 2 schematically illustrates a general structure of the airtreatment unit 200 of WO 2018/002710. The air treatment unit includes areaction reservoir 220, which contains a purifying solution 238. Thesolution is fed, when necessary, from 3 sub-reservoirs: a firstsub-reservoir 226 containing a first reagent (in liquid or solid form),a second sub-reservoir 228 containing a second reagent (in liquid orsolid form), and optionally a third sub-reservoir 230 containing water(H₂O). It should be noted that in some cases, each of the reagent'sreservoirs may contain the respective reagent dissolved inwater—therefore, a separate reservoir for water may not be necessary.When mixed in specific proportions, the substances stored in the threesub-reservoirs form the purifying liquid 238 within the reactivereservoir 220. More than one of the reagents may be supplied to thereaction reservoir as necessary in response to information obtained fromone or more sensors (not shown). Air treatment unit 200 includes acontroller 234 and one or more sensors, including, for example, airsensors, a pH sensor, and fluid level sensor to measure the level offluid within the reaction reservoir, etc. Controller 234 initiates,using blower B (or an air pump or a similar device) a flow ofcontaminated room-air 242. The room air, entering through inlet 224, ispushed against a perforated membrane 236. The perforated membraneconverts the air stream to bubbles 222 that are introduced into thepurifying solution 238 within reservoir 220. While flowing through thepurifying solution, the contaminated air in the form of bubblesinteracts with the reservoir's liquid 238 and is enriched with oxygen.The oxygen-enriched air is then returned to the room as purified air 246via outlet 232. WO 2018/002710 discusses various embodiments andparameters of unit 200 and, in particular, demonstrates how the airtreatment unit 200 can purify air that is heavily contaminated due tofire. However, purification in the case of fire is substantiallydifferent in several aspects from the purification of an everydaycondition air in a room, as discussed by the present invention. Morespecifically: (a) WO 2018/002710 lacks detailed discussion nordemonstrates how airborne bio-hazards can be eliminated; (b) theconcentration rate of airborne bio-hazards in typical room air (as dealtby the present invention) is several orders lower than the concentrationof noxious gases in a case of a fire; (c) there is no discussion in WO2018/002710 as to the system's compactness to a room purifier, nor to apossibility of its integration with traditional home air purifiers; and(d) there is no discussion as to how a single home air purifier of theinvention can eliminate bio-hazards from a plurality of rooms.Additional aspects that differentiate between WO 2018/002710 and thepresent invention are discussed hereinafter.

FIG. 3 a shows a stand-alone home air purifier according to anembodiment of the present invention. FIGS. 3 b and 3 c are twoside-views of the home air purifier presented in FIG. 3 a . The reactor310 is similar in structure to the reactor R of WO 2018/002710, withmodifications (such as in holes size and inter-hole distances) toefficiently eliminate bio-hazards. FIGS. 3 a to 3 c show severaladditional components of the system, as follows: an optional HEPA filter342, a safety valve 312, a cartridge 316 for reagent B in liquid form(H₂O₂ solution; a similar cartridge for reagent A (MOH) is not shown), apump 314 for reagent B (similar pump for reagent A is not shown), ablower 318, electronics box 326, valve 333, battery 324, and a stand330. The dimensions of the stand-alone bio-hazards purifier aretypically on the order of: diameter 20-40 cm and height 70-140 cm. Inthis purifier structure, the reagent cartridges may suffice, forexample, for several months operation period (the actual durationdepends on the pollution level). The optional inclusion of a HEPA filter342 within the stand-alone home air purifier 200 (having a reactionreservoir 220) provides the elimination of small particles, in additionto the elimination of airborne bio-hazards. While the reaction reservoir220 can also eliminate particles (in addition to eliminating bio-hazardsand undesired gases), the tandem structure and separation of the twotasks are more efficient and cost-effective.

In the structure presented in FIGS. 3 a-3 c , the contaminated air isinjected from the bottom into reactor R, through the perforated membrane236, as also shown in FIG. 2 . The reactor's capability to efficientlyeliminate bio-hazards (as well as other gases and solid particles) isproportional to the time of exposure of the bubbles 222 to the purifyingsolution 238. In a reactor into which the air is fed through the bottom(see FIG. 2 and FIGS. 3 a-3 c ), the duration of exposure of each bubbleto the reactive solution is the time it takes a bubble to stay in theliquid, namely from the time it leaves the perforated membrane 236 tothe time it reaches the top surface of the liquid 238 (the time it takesthe bubbles to travel the distance d in FIG. 2 ). This exposure periodenforces a minimal depth of liquid 238 within the reactor for theprocess to be effective and, in turn, enforces a minimal height of thepurifier device 300.

FIG. 4 illustrates a reactor 400 with a structure that provides anextended exposure time of bubbles for a given amount of purifyingsolution, according to the invention's second embodiment. The reactor400 has a top inlet 424 for the contaminated air. Blower 456 suckscontaminated air into an air channel 458, which ends with a funnel 452at its bottom. A perforated membrane 436 positioned within funnel 452 isalways dipped in the purifying solution 438 during operation. The flowof contaminated air 422, upon interaction with the perforated membrane436, produces bubbles below the funnel. Naturally, the bubbles try toescape from solution 438. A backward (upward) passage of bubbles throughthe perforated membrane 436 is blocked by downward air pressure due tothe contaminated airflow. A suitable downward air pressure (above acertain threshold) causes the bubbles to go down and out of theperiphery of funnel 452 and then go upward towards the top of solution438. This non-direct passage that each bubble makes within the purifyingsolution 438 is a substantially longer passage than the direct passage dthat the bubbles make in reactor R presented in FIG. 2 . Therefore, amore efficient purification can be obtained by a given level of liquid,a fact that enables reduction of the dimensions of the liquid reservoir462 and enables compactness of the entire device, as is preferable.Before leaving the purifier 400 through outlet 432, the air passesthrough a demister 446, which removes from the air residues of aerosoland droplets of reactive liquid that the airflow may carry. Cartridge410 contains the H₂O₂ solution (reagent B), and cartridge 412 containsthe MOH solution (reagent A). In this specific case, cartridge 412disperses the MOH solution into the incoming airflow 466 rather thandirectly to the purifying solution 438. Dosing pumps 446 and 448 drivethe liquids from cartridges A and cartridge B, respectively, usingvalves 414, for closing or opening the cartridge supply. These pumps areused to maintain the desired proportion of mixture within solution 438and to adjust this proportion based on real-time measurement of thecontamination level in the room air or according to the user'spreferences. The literature attests that there is a correlation betweenthe amount of CO₂ in a room and the level of airborne bio-hazardcontaminants in that room. Therefore, purifier 400 determines the levelof bio-hazards in the room using a relatively simple and inexpensive CO₂sensor 464. Controller 435 may use a predetermined lookup table oralternative means to translate the CO₂ concentration to the expectedconcentration of airborne bio-hazards. Controller 435 may also useanother lookup table to define the proportions of the ingredients in thereactive solution (and possibly other operational parameters).

In one embodiment of the invention, controller 435 may periodicallydrain the entire purifying solution 438 into a waste container 454 andrenew the solution by fresh content from cartridge A, Cartridge B, andwater. In some cases, one or more of the cartridges contains aqueous MOHand/or aqueous H₂O₂. Therefore a separate cartridge for water may not benecessary. The inventors have found that the structure presented in FIG.4 with the top feeding of contaminated air provides an additionaladvantage compared to the bottom-feeding structure presented in FIG. 2 .It was found that during extended use, bicarbonate accumulates on theperforated membrane 236, which therefore requires periodical cleaning orreplacement. This phenomenon has been eliminated or significantlyreduced in the top feeding structure presented in FIG. 4 . Moreover, ithas been found that the top-feeding structure is quieter compared to thebottom-feeding structure presented in FIG. 2 .

Also shown in FIG. 4 :

-   a. Electronic unit 434, which includes, among other components, a    controller 435, a control panel, a display, and a power supply. The    Electronic unit may also include a Wi-Fi transceiver to allow a    remote control via a smartphone, tablet, etc.;-   b. Sensor 464 to measure the concentration of CO₂ in the room, whose    level measurement assists the controller in deciding when to    activate or deactivate the operation;-   c. Casing 450; and-   d. Some additional sensors, e.g., P (pressure fall), T    (temperature), RH (room humidity) sensors, etc.

FIG. 5 illustrates an integration of the airborne bio-hazards purifier600 of the invention with a traditional filter-based home air purifier100, to form a unified air purifier 700. The bio-hazards purifier 600has a configuration of any of the inventive structures of the inventiondescribed above, including at least the reactor R and its associatedcomponents. The main air blower B₁ of a traditional air purifier 100,built to remove airborne particles, sucks air from the room via inlet610 and directs it towards filter F of the traditional purifier 100,which in turn captures the particles using its HEPA filters. Blower B₂within the airborne bio-hazards purifier 600 of the invention sucks airfrom air-channel 610 a into purifier 600 via the air channel 620,branching out from channel 610 a. The air coming from branch 620 is thenpurified by reactor R in the manner described above. The air purified byreactor R is outputted into branch 620 b, directed into the main channel610 b, and combined with the flow of purified air produced by thetraditional purifier 100. The combined airflow returns double-purifiedair through air-channel 610 b to the room. The two air purifiers 100 and600 may be positioned within the same casing or in two separate casings.The structure presented in FIG. 5 , therefore, enables the use of arelatively small air blower B₂ (for example, 100-1000 liters per minute)in the bio-hazards air purifier 600, utilizing the massive air blower B₁of the traditional air purifier 100 (which typically produces an airflowof 1000-6000 liters per minute), for the distribution of the purifiedair to all parts of the room. Alternatively, the purifier of theinvention may operate independently, while including an internal HEPAfilter, as described below in the embodiment of FIGS. 16 a -16 p.

The airborne bio-hazards purifier of the invention was tested. Thepurifier of the invention significantly reduces the level of bio-hazards(such as viruses and bacteria) in the air and reduces other toxic gases,such as CO₂, CO, formaldehyde, etc.

FIG. 6 shows a mobile home air purifying system, according to anotherembodiment of the invention. The system includes a mobile air purifier710, a docking station 712, a plurality of room sensing units 714, ahome Wi-Fi router 716, and an optional application in a user'ssmartphone 720. Each sensing unit 714 is installed in a single room ofthe house, measuring the air contamination level within that room. Themeasured contamination level may relate to an undesired amount of anygas, particles, airborne bio-hazards, etc., and these levels ofcontaminants may either be measured directly or deduced indirectly basedon any given conversion method. Each sensing unit reports, for example,via a Wi-Fi network, the level of contamination it measures to thedocking station 712, which in turn collects these measurements, andcompares them to one or more predefined thresholds. The docking stationincludes predefined rules for activating the mobile air purifier. Theserules may apply to all rooms, or specific rules may apply to differentrooms. The mobile purifier 710 includes a navigation system, enablingthe purifier to automatically navigate to any of the rooms based oncommands received from the docking station. For example, the dockingstation may convey a command to the mobile purifier to move to abedroom, work there for 60 minutes, and then return to the dockingstation. Following the reception of such command, the mobile purifierautomatically navigates to the specified room, operates for theprescribed duration, and returns autonomously to the docking station.The docking station may also define for the mobile air purifier anyspecific mode of operation and may also send commands to the purifierwhile in operation. The docking station may also serve as a rechargerfor the mobile purifier's 710 battery. The air purifier may include oneor more types of purification units, such as, for example, one or moreHEPA filters and the bio-hazards purification system of the invention asdescribed above.

FIG. 7 shows an exemplary configuration of the system of FIG. 6 for theelimination or reduction of bio-hazards. The mobile air purifier 710 ispreferably made as compact as practically possible. Therefore, mobileair purifier 710 may include a minimal amount of purification solutionwithin a compact-size reservoir 738. The docking station may include oneor more tanks for water and reagents A (MOH) and B (H₂O₂), for drainingthe purification reservoir 738, and refilling it from the tanks. In theexemplary configuration presented in FIG. 7 , the docking stationincludes a filling tank 742 for water and a filling tank 744 for reagentA (MOH). Thanks to its small volume, tank 746 of reservoir B (H₂O₂) isentirely contained within the mobile purifier 710.

Periodically, or based on any other definition, the docking station 712is activated to drain the existing liquid from reservoir 738 of themobile air purifier into sewage tank 748, and refill reservoir 738 withnew liquids (or solids, as is applicable) from tanks 742, 744, and 746(in predetermined proportions). The docking station and the mobile airpurifier include additional components, such as pumps, valves, etc., toperform these tasks. The mobile air purifier also includes a blower forcirculating air into the reservoir (in the form of bubbles, asdescribed) and release it into the room.

The components that are required for the navigation may be dividedbetween the mobile purifier and the docking station in various possibleconfigurations. In one embodiment, the mobile purifier 710 maintains afull navigation capability (i.e., map of the house, etc.). The dockingstation can indicate the targeted room, and based on this indication,the mobile purifier navigates autonomously to the targeted room. Inanother configuration, the navigation capabilities are maintained withinthe docking station 712, while it sends real-time direction commands,such as right, left, forward, backward, move, stop, etc., to the mobilepurifier.

The system may also include a remote control (for example, usersmartphone 720). The remote control may define various parameters of thesystem.

As noted, the system preferably utilizes the Wi-Fi router of the housefor communication between all its components. Other types of wirelessnetworks may be used. Moreover, a central computer, which may beseparate from the docking station, may be utilized to receive sensors'data and send commands to the mobile device. In such a case, the dockingstation serves only as a recharging station for the mobile air purifier.

FIG. 7 shows a configuration that is specifically designed to purifyairborne bio-hazards. This configuration also includes an optional HEPAfilter 752. In other embodiments, the mobile purifier 710 may includeonly airborne bio-hazards purifying capabilities or only HEPA filtersfor eliminating solid particles from the air.

FIG. 8 shows an exemplary docking station 712 and a mobile purifier 710.The relative dimensions may vary.

FIGS. 16 a-16 p illustrate a structure of a home-purifier 800, accordingto a third embodiment of the invention. FIGS. 16 b and 16 c areschematic diagrams. FIGS. 16 h, 16 i, and 16 j provide partialillustrations, respectively, of the home-purifier. FIGS. 16 e, 16 f, and16 g provide cross-sectional views of the home-purifier. FIGS. 16 k-16 ndescribe the structure of the perforated membrane of the home-purifier800, and FIGS. 16 o and 16 p describe the improved effect of bubblecreation obtained by the perforated membrane of the invention comparedto a conventional perforated membrane.

FIG. 16 a shows the external shape of the home-purifier 800 (thisexternal shape is provided as an example, for illustration only). FIG.16 b generally illustrates the operation of the reactor Ra of thehome-purifier 800. The general structure and operation of reactor Ra aresomewhat similar to the structure and operation of the bottom-fed priorart reactor R of FIG. 2 (similar references within the figures relate tosimilar elements)—the differences between the two reactors areelaborated below. However, while in reactor R of FIG. 2 , thecontaminated air inlet 224 is positioned at the bottom of the reactor,the respective air inlet 824 of reactor Ra is positioned at the top ofthe purifier. The contaminated air is received at top inlet 824 andconveyed downwards via air pipe 827 into a sump 837. Air pipe 827arrives at the sump via a central opening at the perforated membrane836. The contaminated air is pressurized within the sump, passingbottom-up through the perforated membrane 836, causing bubbles withinthe solution 838. The bubbles interact with the reservoir's liquid 838and are enriched with oxygen. The oxygen-enriched air is then returnedvia a demister and carbon filter (not shown) to the room as purified air877 via outlet 832.

FIG. 16 c schematically illustrates the structure of purifier 800. Insimilarity to the scheme of FIG. 5 (similar references relate to similarcomponents), Blowers B₁ and B₂ simultaneously suck contaminated air fromthe room via inlet 824. After passing a Hepa filter 842, the airflow isdivided into air channels 819 and 829, respectively. Air channel 819returns Hepa-filtered air to the room in similarity to a conventionalfiltering device (via blower B1), while air channel 829 conveys air intoreactor Ra (via blower B2) for purification. The contaminated air, whichis top-to-bottom conveyed into sump 837 (see FIG. 16 b ), passes fromthe sump in an upward direction via the perforations of perforatedmembrane 836, creating bubbles within solution 838, performingpurification following interaction between the bubbles and the solution(in a manner as described above). Solution 838 occupies a portion of thespace of the reactor compartment (above the solution, there is a gasspace). Following the purification, the purified air passes firstthrough demister 846, which removes from the purified air residues ofaerosol and droplets of the reactive liquid that the airflow may carry.From the outlet of demister 846, the purified air is conveyed tooptional carbon filter 849, which removes smells from the air. From theoutlet of the carbon filter, the purified airflow merges with theHepa-filtered airflow 819 to form a unified airflow 819 a, which isconveyed to the outlet 832 (i.e., back to the room). Cartridge A (alkalihydroxide, e.g., sodium or potassium hydroxide) is provided in a tabletform; each tablet is individually dropped into solution 838 by atablets-feeder 841. A liquid (hydrogen peroxide) contained withincartridge B is fed into solution 838 utilizing (peristaltic) first pump839. The feeding of the cartridges' contents into the solution may beperformed, respectively, either periodically or every predefined periodof the reactor operation. The purifier further includes a clean/wastewater container 847. Initially, cleaned water is filled into container847 and conveyed into reactor Ra to form solution 838. Periodically, orafter a predefined period of operation, solution 838 is pumped utilizingsecond pump 857 into container 847 for removal from the device andsolution refreshment. The Hepa filter 842, clean/waste water container847, carbon filter 849, cartridge A 826, and cartridge B 828 areremovable/replaceable components. The entire system is controlled bycontroller 801.

FIG. 16 d shows the general assembly structure of purifier 800. Thepurifier generally has a cylindrical configuration, and it includes(from bottom to top) a reactor unit 850, operational unit 860, andstorage unit 870. Also shown are Hepa filter 842, main blower B1, andcover 851.

Reference is now made particularly to FIGS. 16 e, 16 h, and 16 j . Thestorage unit 870 is removable, containing the solution ingredients, suchas (a) tap water, (b) alkali hydroxide (potassium hydroxide or sodiumhydroxide, respectively) in a solid form (or otherwise), and (c) H₂O₂(hydrogen peroxide) in liquid form. The storage unit (in this specificexample) includes 3 concentric containers, as follows: Cartridge Acontainer 826 for the alkali hydroxide (NaOH, KOH or both, (in a tabletform), water container 847, and H₂O₂ container (cartridge B) 828.Cartridge A is divided into a plurality of column cylinders 826 a, eachcontaining a plurality of tablets. In an embodiment of the invention,the plurality of hollowed column cylinders 826 a are arranged in arevolving drum 826. To add a tablet to solution 838, a motor (not shown)rotates the drum 845 to angularly position a tablets' column 626 a aboveopening 859 (best shown in FIG. 16 g ), permitting one tablet to fallinto solution 838 gravitationally. The structure of the reactor is shownmainly in FIGS. 16 e, 16 f, and 16 i , and the structure of theperforated membrane 836 is shown mainly in FIGS. 16 k, 16 l , and 16 n.

For example, the weight of each tablet may be about 5 to 100 g, e.g.,from 15 to 30 g, and 2 to 100 tablets may be included within cartridge826. The water container may contain 1 to 10, e.g., 2 to 6 liters, andthe hydrogen peroxide container may include between 250 ml and 10 liter.Initially, the user removes the storage unit using handle 863 and fillsit with the solution ingredients. Upon filling the water container withtap water, and filling cartridges A 826 and B 828 with tablets andliquid, respectively, and remounting the storage unit at the purifier,the device is ready for operation. The water is poured down to thereactor via pipe 853, and one tablet (or more, if necessary) is droppeddown to the solution via opening (and respective pipe) 859. A dose ofthe hydrogen peroxide is conveyed periodically into proximity of theperforated membrane utilizing pump 839, pipe 855 (one or more pipes maybe used), and respective perforations (not shown) on tube 855 a (FIG. 16f ). It has been found that supplying the hydrogen peroxide near theoutlets of the membrane-perforations 836 a is preferable, as itsignificantly reduces, even eliminates clogging of the membraneperforations due to carbonates that accumulate in the solution duringthe process. Membrane 836 is positioned slightly above thebottom-internal surface of the device, creating a sump 837 (see FIGS. 16b and 16 e ) below the membrane. The contaminated airflow, as suckedfrom the room by blower B2 (FIG. 16 c is conveyed via intake pipe 829,arriving at sump 837 via central opening 836 b of membrane 836.

During the process, air from the sump penetrates solution 838 via themembrane's 836 perforations, creating bubbles that interact with thesolution as described above. The bubbles leave the solution as apurified air. The purified air passes through demister 846, whichremoves from the purified air residues of aerosol and droplets of thereactive liquid that the airflow may carry. The outlet of the demisterincludes a funnel (not shown), which is connected to a pipe (not shown)leading to the carbon filter 849.

After some period of operation, the effectiveness of solution 838reduces to a degree requiring entire replacement by fresh water andingredients from cartridges A and B, respectively. When such a necessityarose, pump 857 pumps and conveys the entire liquid content ofcompartment 820 (FIG. 16 b ) to the waste/clean water container 847. The“waste” liquid is typically rich in potassium carbonate (not a hazardousmaterial). The user may then remove the storage unit 870 and may either:(a) use the “waste” liquid to fertilize his garden; (b) pour the liquidinto the sewerage; or (c) return the liquid to the ingredients' supplierfor further processing.

The inventions' process is optimized when as small as possible and asmany as possible bubbles are simultaneously created. This configurationmaximizes the overall interaction surface between the bubbles andsolution 838. However, it has been found that a membrane with too closeperforations results in vast merges of proximate bubbles, as illustratedin the prior art membrane 896 of FIG. 16 o . The inventors have foundthat the difficulty that individual bubbles face (in prior artmembranes) when trying to separate from the membrane top facet towardsthe solution increases the size of the bubbles, leading to a mergebetween proximate bubbles. This delay of separation increases the sizeof individual bubbles to a situation where proximate bubbles merge.

FIG. 16 n shows a cross-section of membrane 836, resolving the aboveproblem of the merge between bubbles. In contrast to a cylindricalperforation' cross-section, as existing in typical membranes, eachperforation of the invention's membrane includes two sections, a lowercylindrical section 836 c and an upper frustoconical section 836 dexpanding towards the top surface of the membrane. More specifically,the bottom-to-top airflow first faces a small-diameter cylindricalperforation, and then the perforation diameter expands towards the topsurface of the membrane. Such a perforation configuration eases theseparation of each bubble from the perforation, thereby significantlyreduces merges between bubbles for a given perforation-dimension andperforations density. FIG. 16 p illustrates such an improved resultcompared to the cylindrical configuration of FIG. 16 o . As shown, inthe cylindrical configuration of FIG. 16 o , proximate bubbles 836 gtend to merge before their release to the solution. On the contrary tothe cylindrical configuration of FIG. 16 o , in the combinedcylindrical-frustoconical configuration of FIG. 16 p , the occurrence ofmerges between bubbles 936 g is reduced, even eliminated.

In some cases, the height of the lower cylindrical section of theperforation is reduced (compared to the upper conical section's height).In some other cases, the lower cylindrical section of the perforationmay be eliminated, resulting in a truncated cone cross-section. FIG. 16k shows a top view of membrane 836, FIG. 16 l shows the membrane inperspective view, and FIG. 16 m shows a bottom view of the membrane. Ascan be seen, each perforation at the bottom side of the membrane has asmaller diameter compared to its respective diameter at the top side.For example, the diameter at the bottom surface of the membrane may bebetween 0.08-1 mm. The perforation's diameter at the top surface may be1.3 to 2.0 larger than the bottom diameter. The distance betweenindividual perforations is in the range of 2-50 of the perforation'sdiameter at the upper surface of the membrane. The above-described flatperforated membrane, with the combined geometry of perforation shaped ascylindrical sections joining frustoconical sections, forms anotheraspect of the invention. It can be produced by 3D printing.

Purifier 800 may be stationary, mobile (in similarity to embodiment700), or manually carried from one room to another.

FIGS. 18 a-18 d show a fourth purifier embodiment 900 of the invention.This embodiment is somewhat similar to the embodiment of FIG. 4 , wheresimilar references within figures respectively refer to similarelements. For the sake of brevity, those similar elements andfunctionalities are repeated herein. In similarity to the embodiment ofFIG. 4 , contaminated air is fed via inlet 924 into inlet air channel958. The inlet air channel leads into horizontally-disposed spiralperforated tubing 936, positioned proximate to the bottom of the liquidreservoir compartment 962, however, somewhat spaced apart from thebottom of the reservoir. The perforations 936 b along the spiral tubing936 have a diameter in the range from, e.g., 0.08 mm to 1.0 mm anddistance between individual perforations in the range of 2-50 of theperforations diameter. FIGS. 18 c and 18 d show a cross-section of onetube of perforated spiral tubing 936. The perforations 936 b are locatedalong the periphery of the tube in cross-section at an angle α typicallygreater than 30° downwards relative to the horizontal. As a result ofthis arrangement, the bubbles are “injected” from the spiral tubing 936to the solution in a downwards direction. Therefore, before goingupwards towards the top surface of the solution, each bubble 936 g firstgoes downwards. This arrangement, therefore, increases the route andrespective interaction period between each bubble and the solution,before the bubble is released from the solution. In such a manner, thepurification efficiency of the reactor is improved, and this feature isparticularly important in a home purifier having small dimensions and alimited amount of a purifying solution.

Another aspect of the invention involves modifying the indoor airtreatment program offered by the MOH/H₂O₂ reactor described above, byincorporating a CO₂ adsorption scrubber upstream of the MOH/H₂O₂reactor. A battery consisting of CO₂ adsorption scrubber and MOH/H₂O₂reactor offers greater versatility in coping with changes in CO₂ levelsin the room, and better management of alkali hydroxide and hydrogenperoxide feed supply to the reactor, because the battery can switchbetween different modes of operation, depending chiefly on factors suchas CO₂ level in the room and presence of occupants in the room. The CO₂adsorption scrubber and MOH/H₂O₂ reactor may be designed to operate withairflows supplied at different volumetric rates (high and low,respectively).

Reduction of CO₂ levels in indoor air can be achieved in different waysusing a battery consisting of CO₂ adsorption scrubber and MOH/H₂O₂reactor:

1) by the action of adsorption scrubber alone: indoor air is passedthrough the scrubber; CO₂ is captured and held for some time in thescrubber. During that period of time, air with improved quality issupplied to the room from the scrubber. The scrubber is discharged byreleasing CO₂ to the room, e.g., overnight.

2) by the action of MOH/H₂O₂ reactor alone: indoor air is guideddirectly to the MOH/H₂O₂ reactor, bypassing the adsorption scrubber; CO₂is transformed into harmless carbonate/bicarbonate salts; air withimproved quality is supplied to the room from the reactor.

3) by a combined mode of operation: indoor air flows through thescrubber over a period of time during which the MOH/H₂O₂ reactor is atrest. CO₂ is captured and held in the scrubber but after a while theMOH/H₂O₂ reactor enters into service such that CO₂ discharged from thescrubber is directed to, and mineralized in, the MOH/H₂O₂ reactor.

Accordingly, one aspect of the invention relates to the combined mode ofoperation outlined above, i.e., by capturing and holding CO₂ is anadsorption scrubber, and after a while, discharging the CO₂ from thescrubber and mineralizing the CO₂ in the MOH/H₂O₂ solution, i.e., to amethod of improving indoor air quality, comprising:

providing airflow through CO₂ adsorption scrubber over a first period oftime to capture CO₂ by an adsorbent in the scrubber while reintroducingCO₂-depleted air from the scrubber into a room; desorbing CO₂ from theadsorbent during a second period of time (for example, by heating theadsorption scrubber to reach desorption temperature) while guiding airladen with the desorbed CO₂ from the scrubber into a gas/liquidcontactor charged with aqueous alkali hydroxide/H₂O₂ solution, passingthe CO₂-laden air through a perforated membrane installed in thegas/liquid contactor below the surface level of the aqueous alkalihydroxide/H₂O₂ solution, such that bubbles produced travel through saidsolution, and getting treated air with reduced CO₂ level from saidgas/liquid contactor.

Another aspect of the invention is an air purifier based on a batteryconsisting of CO₂ adsorption scrubber and MOH/H₂O₂ reactor, which canimprove indoor air quality by the three options set out above. In itsmost general form, the air purifier comprises:

a device used to move air, e.g., a blower or a fan, for supplyingcontinuous air flow through the air purifier;

CO₂ adsorption scrubber;

a gas/liquid contactor located downstream of the scrubber;

an outlet pipe to release air from the air purifier to the room; a firstairflow line connecting the blower or the fan, to the outlet pipe,configured to direct incoming air stream to the adsorption scrubber, andoutgoing air stream from the scrubber to the outlet pipe;

a second air flow line connecting the blower or the fan to the outletpipe, configured to direct incoming air stream to the gas/liquidcontactor, and outgoing air stream from the gas/liquid contactor to theoutlet pipe; and

a third air flow line connecting the blower or the fan to the outletpipe, configured to direct incoming air stream to the adsorptionscrubber, and outgoing air stream from the scrubber to the gas/liquidcontactor;

an array of valves to guide the moving air through said first, second orthird air flow lines;

and optionally a heater positioned downstream to the adsorptionscrubber.

FIG. 20 shows a preferred design of an air purifier of the invention.The method of operation will be described in reference to FIG. 21 ,which shows the same elements of FIG. 20 .

A blower (1) provides airflow through the air purifier, capable ofsupplying volumetric flow rate of 100-2000 litre/min, adjusted to fitthe selected mode of operation, as explained below. The airflow movesvia, e.g., 15-50 mm diameter conduits installed in the air purifier, andis directed to the air outlet (9) via a path regulated by the states ofvalves (4), (5), (6) and (7), i.e., after the airflow was passed throughthe adsorption scrubber (2) or the gas/liquid contactor (3).

CO₂ adsorption scrubbers (2) suitable for use in the invention exist inthe marketplace, utilizing physisorption or chemisorption-basedsorbents. A simple design is of a fixed-bed scrubber, usually a verticalcylindrical fixed-bed scrubber, as shown in FIG. 20 . The fixed bed isbased of material(s) known to adsorb CO₂, e.g., materials possessinghigh specific surface area and porous structure, such as activatedcarbon [including activated carbon which was surface-modified toincorporate functional groups with basic character, that is,nitrogen-containing functionalities, as described in Journal ofAnalytical and Applied Pyrolysis 89 (2010), p. 143-151)], carbon fibres,zeolites, molecular sieves, metal organic frameworks, highly porouspolymers and amine-incorporated clay minerals, used in a granular orpellet forms (e.g., mm size), supported on grids and sometimes coveredby a mesh, e.g., single or multilayer structure.

The air purifier may include a heating unit (8) positioned downstream toCO₂ adsorption scrubber (2), in the form of a convection heater in whichan electric heating coil is installed, operating at 100-3000 watt. Togoal served by heating unit (8) is to enable CO₂ adsorption scrubber (2)to switch from adsorption to desorption, i.e., to regenerate the sorbentmaterial after it reached saturation or nearly saturation, by passingheated air through the scrubber. Rise in temperature causes CO₂molecules to detach from the sorbent surface. In the embodiment of theinvention shown in FIG. 21 , a single supply line is used to directincoming air from blower (1) to the adsorption scrubber (2), with heater(8) being positioned on that line. However, a subsidiary pipe may beinstalled, creating a separate path for the heated airflow for thedesorption/regeneration phase, controlled by an additional two-way valve(not shown). But anyhow, heating unit (8) positioned externally toscrubber (2) is not at all mandatory as some adsorption scrubbers arefitted with suitable means to elevate the temperature in the adsorptionscrubber, to switch to desorption mode. Also, more sophisticated designsbased on moving bed or rotating bed configurations, as shown in US2021/025451, can be used.

HEPA filter (not shown) is placed downstream to blower (1) or upstreamto air outlet (9). Whereas blower (1), CO₂ adsorption scrubber (2) andheating element (8) are fairly conventional, the gas/liquid contactor(3) has unique configuration which was described in detail above.

FIGS. 2 and 16B schematically illustrate the key components and featuresassociated with the gas/liquid contactor (3). The major differencebetween the configurations shown in FIGS. 2 and 16B resides in thepositions of the air inlet and air outlet and hence the direction of theairflow through the gas/liquid contactor (upward versus downward airflow in FIGS. 2 and 16 b, respectively).

Perforated membrane is mounted at the lower part of the reactor, belowthe surface level of the MOH/H₂O₂ aqueous solution. One useful design ofthe perforated membrane is shown in FIGS. 16 k -16 p.

FIG. 16 k shows a top view of membrane and holes, FIG. 16 l shows themembrane in perspective view, and FIG. 16 m shows a bottom view of themembrane. As can be seen, each perforation at the bottom side of themembrane has a smaller diameter compared to its respective diameter atthe top side. For example, the diameter at the bottom surface of themembrane may be between 0.08 and 1 mm. The perforation's diameter at thetop surface may be 1.3 to 2.0 times larger than the bottom diameter. Thedistance between individual perforations is in the range of ½ to 1/50relative to diameter of the perforation at the upper surface of themembrane. The role of central opening is explained below.

The unique geometrical motifs of membrane (836) and their useful effectare perhaps better illustrated in FIGS. 16 n, 16 o and 16 p . FIG. 16 nshows a cross-section of membrane (836); rather than having cylindricalcross-section with constant diameter across the membrane thickness, likein typical membranes, each perforation in membrane (836) consists of twosections, a lower cylindrical section (836 b) and an upper frustoconicalsection (836 d) expanding towards the top surface of the membrane. Morespecifically, the bottom-to-top airflow first faces a small-diametercylindrical perforation, and then the perforation diameter expandstowards the top surface of the membrane. Such a perforationconfiguration facilitates the departure of bubbles (836 g) from theperforation, and significantly reduces merges between adjacent bubblesfor a given perforation-dimension and perforations density. FIG. 16 pillustrates such an improved result achieved thanks to the combinedcylindrical-frustoconical configuration, that is, occurrence of mergesbetween bubbles is reduced, even eliminated.

Turning back to FIGS. 2 and 16 b, a vertical cylindrical gas/liquidcontactor (3) is provided with horizontally-mounted membrane (836). Asshown by the schematic illustrations of FIGS. 2 and 16 b, the MOH/H₂O₂solution is supplied by a water tank, a H₂O₂ solution tank (826), andMOH (828). For example, an aqueous alkali hydroxide/H₂O₂ solution issupplied to the gas/liquid contactor either by feeding an alkalihydroxide solution prepared beforehand, or by dissolving solid alkalihydroxide (e.g., in a tablet or granular form) in water suppliedseparately to the gas/liquid contactor, with continuous or periodicaddition of hydrogen peroxide solution to the alkali hydroxide solution.There are benefits to using solid forms of alkali hydroxide and somesetups to enable the addition of MOH tablets into the aqueous solution,e.g., with the aid of MOH tablet cartridge mounted in the gas/liquidcontactor, are described below. Controller (834) is connected to one ormore sensors, e.g., a pH sensor and fluid level sensor to measure thelevel of solution (838), to control feeding rates of the reagents, etc.

In the variant of FIG. 2 , air inlet (224) and air outlet (232) areplaced at the bottom and top sections of the gas/liquid contactor,respectively; a different arrangement is seen in FIG. 16 b , where bothgas inlet (824) and gas outlet (832) are placed at the top section ofthe reactor. In FIG. 16 b , CO₂-laden air enters gas/liquid contactorvia top inlet (824) and is moved downwards through pipe (827) into asump (837). Air pipe (827) arrives at sump (837) via a central opening(836 d) at perforated membrane (836), which is best seen in FIGS. 16k-16 m . The incoming air is pressurized within the sump, passingbottom-up through the perforated membrane (836), creating bubbles (822)within the solution (838). The bubbles interact with the MOH/H₂O₂reagent and are enriched with oxygen. The oxygen-enriched air is thenreturned via a demister and carbon filter (not shown) to the room viaoutlet (832).

FIGS. 16 d, 16 e and 16 j show the incorporation of a water tank, H₂O₂tank and MOH tablets' cartridge into a gas/liquid contactor (800)possessing essentially cylindrical symmetry. It is seen that it ispartitioned into a lower portion (850) and an upper portion (870). Thelower portion of the gas/liquid contactor (800) is a gas/liquidcontacting unit (850) as previously described, i.e., the reaction zonein which CO₂ mixes with the MOH/H₂O₂ solution to undergo mineralization,with membrane (836) installed at the bottom and downwardly extendingpipe (829) arriving at sump (837) via central opening located inmembrane (836), have already been described.

The upper portion of the gas/liquid contactor (870) consists of astorage unit which includes three concentric containers, as follows:Cartridge A container (826) for the alkali hydroxide (NaOH, KOH or both,(in a tablet form), water container (847), and H₂O₂ container (cartridgeB) (828). Cartridge A is divided into a plurality of column cylinders(826 a), each containing a plurality of tablets. In an embodiment of theinvention, the plurality of column cylinders (826 a) are arranged in arevolving drum (845). To add MOH tablet to the reaction zone, a motor(not shown) rotates the drum 845 to angularly position a tablets' column(826 a) above opening accessing the reaction zone, enabling one or moretablet(s) to fall into the reaction zone (850). Hydrogen peroxide issupplied using a pump, via pipe (828 p), below the level of the solution(838). Demister (846) is also included.

For example, the weight of each tablet may be about 5 to 100 g, e.g.,from 15 to 30 g, and 2 to 100 tablets may be included within cartridge(826 a). The water container may contain 1 to 10, e.g., 2 to 6 liters,and the hydrogen peroxide container may include between 250 ml and 10liter.

Turning back to FIG. 21 to describe the operation of the air purifier,there are in fact three major alternatives.

According to the first mode of operation, blower (1) supplies airflowthrough CO₂ adsorption scrubber (2) and moves depleted-CO₂ airflow whichexists the scrubber via air outlet (9) to be reintroduced into the room,by keeping two-way valves (7) and (5) open and two-way valves (6) and(4) closed. The air purifier switches to such mode of operation inresponse to detecting increased CO₂ levels in the room, or is programmedto operate likewise during time periods at which relatively high CO₂levels are anticipated, e.g., when a large number of attendees isexpected, such as when a meeting takes place in the room. Because onlythe CO₂ adsorption scrubber is at service while the gas/liquid isdisconnected, the air purifier can operate with the blower (1) supplyingairflow at a fairly high volumetric flow rate, over short time periods,i.e., a couple of hours or so. When the sorbent material becomessaturated, or after the people (e.g., workers, meeting participants)have left the room, the scrubber regeneration phase may start, e.g.,heating unit (8) is turned on so as to feed the scrubber with hot airand release air laden with CO₂ through air outlet (9). It is noted thatthis mode of operation largely deals with peak CO₂ levels in the room,to produce and constantly reintroduce CO₂-deplated airflow to the roomwhen it occupied by people, without chemically eliminating the CO₂molecules.

According to the second mode of operation, blower (1) supplies airflowthrough gas/liquid contactor (3), i.e., bypassing scrubber (2) and movesdepleted-CO₂ airflow which exists the gas/liquid contactor (3) via airoutlet (9) to be reintroduced into the room, by keeping two-way valves(6) and (4) open and two-way valves (7) and (5) closed. Volumetric flowrates received by the gas/liquid contactor are generally lower thanthose received by the scrubber, just holding CO₂ temporarily in thescrubber (2).

According to the third mode of operation, blower (1) supplies airflowthrough CO₂ adsorption scrubber (2) and moves depleted-CO₂ airflow whichexists the scrubber via air outlet (9) to be reintroduced into the roomover a period of time t₁ during which the MOH/H₂O₂ reactor (3) is atrest, by opening two-way valves (7) and (5) and closing two-way valves(6) and (4). During t₁, CO₂ is captured and held in the scrubber butafter a while the MOH/H₂O₂ reactor enters into service. That is, CO₂ isdischarged from the scrubber (2) and is directed to, and mineralized in,the MOH/H₂O₂ reactor (3), by keeping two-way valve (7) open, turning onthe heater to supply hot air thereby promoting the desorption process ofthe CO₂ molecules from the sorbent in scrubber (2), to produce CO₂-ladenairflow. Two-way valve (5) and (6) are closed whereas two-way valve (4)is open, such that the CO₂-laden airflow is passed through gas/liquidcontactor (3).

CO₂-laden air delivered to gas/liquid contactor (3) over a period oftime t₂, and is forced to flow across the membrane (236) to createbubbles which are caused to travel through the alkali hydroxide solution(e.g., NaOH or KOH, or their mixture), to which H₂O₂ stream isperiodically or continuously added (for example, by injection beneaththe level of the alkali hydroxide solution, in close proximity to theperforated membrane, i.e., in the vicinity of the perforations).Concentration of the alkali hydroxide solution varies from 5% to 481-50%by weight, e.g., from 10 to 48%-50% by weight. The concentration of thehydrogen peroxide solution added to the alkali hydroxide solution isfrom 3%, 4%, or 5% up to 35% by weight, e.g., from 10 to 30% by weight.Acceptable addition rate of the H₂O₂ stream may vary from 0.01 ml/min to10 ml/min, e.g. up to 2, 3 or 4 ml/min. The volumetric ratio between thesolutions in the range of 2:1 to 10:1 in favor of the alkali hydroxidesolution. In the combined mode of operation (CO₂ capture in scrubber(2), CO₂ mineralization in reactor (3)), t₁<t₂, that is, the scrubbercaptures CO₂ during relatively short time periods at CO₂ peak hours,whereas reactor (3) runs the chemical elimination of CO₂ with lowvolumetric flow rate over an extended time period.

EXAMPLES Example 1 Removal of Formaldehyde Vapours from Air byAbsorption to Aqueous Solution of Sodium Hydroxide and Hydrogen Peroxide

The goal of the study was to test the ability of the aqueous NaOH/H₂O₂reagent to remove formaldehyde vapors from air that is passed/bubbledthrough the reagent and decompose the formaldehyde, challengingcharacteristic formaldehyde indoor loading and maintaining adequateformaldehyde conversion rates over a couple of hours.

The experimental set-up is shown in FIG. 9 . Aqueous formaldehydesolution (100 ml of 37 wt. % solution, stabilized with methanol) wascharged into a round bottom flask (1). A cylindrical reactor (4) wascharged with 150 ml of sodium hydroxide solution 30 wt %. The H₂O₂solution was added slowly to the sodium hydroxide solution, at a rateflow of 1 ml/min, over the two hours test period, such that the totalamount of the H₂O₂ solution added was 120 ml. Reactor (4) issubstantially tubular in shape (inner diameter: 9 cm; height: 40 cm). 5mm thick stainless-steel membrane is mounted horizontally inside thereactor, about 2.5 cm from the bottom of the reactor. The pore size ofthe membrane was 147 μm; center to center distance between adjacentpores is ˜50 μm. The level of the liquid in the reactor was 7 cm, i.e.,the membrane was submerged about 4.5 cm below the surface level of thesolution.

The formaldehyde solution was vaporized using hot plate (2) with anaverage temperature of 35° C. and the vapors were led to reactor (4).The peristaltic pump (3) used was operated at 1 m³/min flow rate. Theformaldehyde concentration in the incoming stream was adjusted to0.2-0.3 mg/m³ in air, representing typical contamination level inresidential areas, based on WHO guidelines for Indoor Air Quality. Apair of formaldehyde detectors (5-formaldemeter htv-m, manufactured byPPM technology Ltd., UK) connected to the incoming (contaminated) andoutgoing (purified) streams were used to measure the concentration offormaldehyde, respectively.

Results of characteristic experiments are shown graphically in FIGS. 10and 11 . FIG. 10 is formaldehyde concentration versus time plot,measured for the outgoing treated air stream (concentration is expressedas mg/m³). FIG. 11 is formaldehyde concentration versus time plot,measured for the incoming (contaminated) and outgoing (treated) airstreams (concentration is expressed in ppm). The results indicate stableabsorption and conversion rate of formaldehyde with the aid of theNaOH/H₂O₂ reagent over test period of about two hours.

Example 2 Treatment of Low Concentration CO₂-Bearing Air by Absorptionto Aqueous Solution of Sodium Hydroxide and Hydrogen Peroxide

The goal of the study was to test the ability of the aqueous NaOH/H₂O₂reagent to remove CO₂ from air that is passed/bubbled through thereagent, when the air is loaded with low CO₂ concentrations, challengingcharacteristic CO₂ indoor loading and maintaining adequate CO₂conversion rates over a couple of hours.

The experimental set-up is shown in FIG. 12 . The CO₂ source was acommercial 100% CO₂ held in gas cylinder (1). Pumps (3) made CO₂ fromcylinder (1) and air from cylinder (2) to flow and mix to create acombined stream of 1200 ppm-CO₂ bearing air, which was directed toreactor (4) (as previously described) at a flow rate of 13 L/min, wherethe NaOH/H₂O₂ reagent was held (the reagent was charged to the reactorby first adding 250 ml of 30 wt % of NaOH solution, and slow continuousaddition of hydrogen peroxide solution (10%) at a flow rate of 0.1ml/min over the test period. A pair of CO₂ detectors (5-BGA-EDG-MA,Emproco Ltd., Israel) connected to the incoming (1200 ppm-CO₂ bearingair) and outgoing (purified) streams were used to measure theconcentration of CO₂, respectively.

CO₂ levels in the incoming and outgoing streams were recordedcontinuously over forty minutes. The results are presented graphicallyin FIG. 13 . It is seen that high conversion percentage of CO₂ wasmaintained over the forty minutes test period, reaching 90-100%.

Reaction of CO₂ with alkali hydroxide alone would merely result information of the corresponding carbonate, as shown by the followingreaction equation:

CO₂+2MOH→M₂CO₃+H₂O

In contrast, reaction of carbon dioxide with the superoxide leads toformation of oxygen:

2MO₂+CO₂→M₂CO₃+1.5O₂

Hence, the involvement of the superoxide radical in decomposing of CO₂is demonstrated by evolution of O₂. That is, enrichment of the outgoingair stream with oxygen. Oxygen levels in the incoming and outgoingstreams recorded over forty minutes indeed indicate oxygen evolution andcreation of oxygen-rich outgoing air stream, as shown by the O₂concentration versus time plot of FIG. 14 , indicating from 22 to 28%oxygen level.

Example 3 Reduction of Microbial Load in Air with the Aid of AqueousSolution of Sodium Hydroxide and Hydrogen Peroxide

The goal of the study was to investigate the biocidal action ofNaOH/H₂O₂ reagent on contaminated air, that is, to achieve reduction ofmicrobial load of indoor air, e.g., by removing bacteria such asMicrococcus luteus, Bacillus and Clostridium. The initial load was 1*10⁸CFU/ml for each of the bacteria species tested (which is approximatelyequal to 400 CFU/plate contaminated air).

The Experimental set-up is shown in FIG. 15 . Reactor (1) is loaded withdissolved bacteria (received from Aminolab). Reactor (4) (as previouslydescribed) is charged with the NaOH/H₂O₂ reagent. The reagent wasintroduced into reactor (4) by addition of 100 ml of NaOH (30 wt %), andslow addition of 40 ml H₂O₂ (at a rate of ˜2 ml/min, over the testperiod). The pair of reactors were identical in shape and size: bothwere cylindrically shaped with length of 50 cm and diameter of 10 cm,designed to enable upwardly flowing air to pass therethrough. Air wasmade to flow by pump (3) from air chamber (2) at flow rate of 13 L/minthrough reactor (1), to produce an outgoing contaminated air stream thatwas guided to, and forced to bubble through, the aqueous reagent inreactor (4) (the height of the liquid in the column is 7 cm).

Biocide contact time was fifteen minutes. A sealed containeraccommodating six petri dishes was used to receive the treated airexisting reactor (4) after the fifteen minutes elapsed. It was foundthat 15 minutes of exposure to the superoxide radical (active solution)achieved reduction of bacteria concentration to 2 CFU/plate, indicatingconversion rate of 99.51.

Example 4 Reduction of Microbial Load in Air with the Aid of AqueousSolution of Sodium Hydroxide and Hydrogen Peroxide

Experimental Set-Up

The experimental set-up is shown in FIG. 17 . It consists of three majorparts:

(A) a mixing unit, where an air stream is loaded with biologicalcontamination.

(B) a treatment unit, i.e., a gas-liquid contactor, where thebiologically contaminated air stream is treated with the aqueousMOH/H₂O₂ solution.

(C) a filtration and sampling unit, where condensable samples arecollected; the so-formed solutions are then analysed (to count themicroorganisms that survived the treatment).

The Mixing Unit (A)

Air stream from an air compressor (1) is passed through an air filter(2) before it enters a mixing chamber (4) at a pressure of 5 bars (flowrate of about 100 L/min). The air feed line is equipped with a regulatorand a flowmeter (3) to adjust the air flow rate. Syringe pump (7; NE-300Just-Infusion™, by New Er Pump Systems Inc.) delivers a microbialsuspension to a bioaerosol generator (6; Blaustein atomizer (BLAM), amulti-jet model by CH technologies), where it becomes small and lightenough to be carried on air. The BLAM atomizer is installed insidemixing chamber (4), discharging the bioaerosol at the lower portion (5)of mixing chamber (4), at a flow rate of 6 L/min, where the bioaerosolis loaded onto the compressed air fed to chamber (4), creatingbiologically contaminated air stream. Chamber (4) is also provided witha jet nozzle port (not shown) to introduce a disinfectant (6-10%hydrogen peroxide solution) and a secondary air stream, creating adisinfectant aerosol to clean the interior of chamber (4) between thetests. An outgoing, biologically contaminated air stream flows fromchamber (4) to the treatment zone at about 106 L/min.

The Treatment Zone (B)

A reactor, i.e., a gas-liquid contactor, where the biologicallycontaminated air is mixed with the aqueous reagents MOH/H₂O₂, isindicated by numeral (8). Reactor (8) is tubular in shape (innerdiameter: 9 cm; height: 40 cm). 5 mm thick stainless steel membrane (9)is mounted horizontally inside the reactor, about 2.5 cm from the bottomthe reactor. The pore size of the membrane was 147 μm; centre to centredistance between adjacent pores is ˜50 μm. Sodium hydroxide (30% byweight solution) and hydrogen peroxide (10%-30% by weight solutions) areheld at tanks (11) and (12), and are supplied to reactor (8) usingperistaltic pumps operated under controllers 15 and 16. The NaOH andH₂O₂ aqueous streams enter the reactor (8) through openings located atthe lateral surface of the reactor, below the level of the membrane (9).A third peristaltic pump C (not shown) is installed to discharge theexhausted aqueous reagent from the bottom of reactor (8) to a waste tank(not shown). Numeral (10) indicates the surface level of the aqueousreagent added to the gas-liquid contactor (8). An outgoing disinfectedair stream (13) flows to the filtration and sampling unit.

The Filtration and Sampling Unit (c)

The filtration and sampling unit (3) consists of a dry filter airsampler (14); ACD-200 Bobcat). The air effluent of reactor (13) ispassed through the Bobcat sampler (controlled by (17)) which generatesliquid samples for analysis. That is, the collected fluid is withdrawnfrom the Bobcat sampler and samples (5-7 ml) are incubated to detect andcount the microorganism. The experimental set-up is mounted inside ahood, such that air sampler (14) is fed with the treated air stream (13)delivered from reactor (8) with minimal ambient air interference.

Experimental Protocol

The strain of bacteria chosen for the tests was Kocuria rhizophila (ATCC9341). It is readily visible when grown on agar plate, owing to itsspherical morphology and intense yellow color. TSB was used as a culturebroth to grow the bacteria (overnight, at 30-35° C.).

Each session consisted of the following experiments:

One negative control experiment, in which purified water is injectedfrom the syringe pump (7) to the aerosol generator (6), creating asterile aerosol that is discharged to chamber (4), where it is mixedwith incoming sterile air stream. The outgoing air/aerosol stream flowsto reactor (8). Reactor (8) operates under dry conditions, i.e., the airstream is not contacted with a liquid whatsoever. The aerosol moves tothe Bobcat sampler (14), condensed, collected and tested for thepresence of the bacteria (no bacterial growth was to be detected in asuccessful run).

Two or more test experiment, in which a microbial suspension is injectedfrom the syringe pump (7) to the aerosol generator (6), creating abioaerosol that is discharged to chamber (4), where it was mixed withincoming sterile air stream. The air/bioaerosol stream from chamber (4)flows to reactor (8); it enters reactor (8) from the bottom, flows in anupward direction across the aqueous NaOH/H₂O₂ solution. The outgoing,disinfected air/aerosol stream flows from the top of reactor (8) to theBobcat sampler (14), samples are condensed, collected and tested for thepresence of the bacteria. The combinations of NaOH/H₂O₂ aqueoussolutions added to reactor (8) are tabulated below:

TABLE 1 Treatment A1 A2 NaOH 30% solution 3.0 liter 3.0 liter H₂O₂ 10%solution 0.3 liter H₂O₂ 30% solution 0.3 liter

One positive control experiment, which only differs from the testexperiment in that reactor (8) was filled with purified water in placeof the active NaOH/H₂O₂ solution. The positive control experiment showedthat the system does not block the passage of microorganism andfunctioned as the positive baseline to which each test was com-pared to,on each session, to evaluate the efficacy of the treatment. Positivecontrol runs were performed once per session, usually after the testexperiments.

System disinfection was performed at the beginning of each session andafter each test involving the passage of microorganisms into the system(see the 6-10 H2O2 disinfectant arrangement mentioned above); i.e.,reactor (8) was drained to discharge the exhausted aqueous reagent, andthe system was cleaned and disinfected. Samples collected were diluted(e.g., 10⁻⁵ dilution), disposed on agar plates to enable CFU counting.

Results

The concentration and total number of CU injected to create thecontaminated biological air stream and removal rates measured (expressedby log reduction units, calculated based on total CFU injected andrelative to the positive control base) are tabulated in Table 2.

TABLE 2 Treatment A1 A2 CFU injected 8.1 × 10⁶ CFU/ml 5.3 × 10⁶ CFU/mlTotal: 4.05 × 10⁸ CFU Total: 2.65 × 10⁸ CFU Log reduction* 3.3-3.95.6-8.4 Log reduction** 1.6-2.2 3.6-6.4 *calculated based on total CFUinjected. **calculated relative to positive control

It is seen that the combined action of alkali hydroxide and hydrogenperoxide achieved high removal rates of the bacteria Kocuria rhizophilafrom air (>99.99% elimination).

Example 5 Inactivation of Human Coronavirus OC43(hCoV-OC43) by theAction of Sodium Hydroxide and Hydrogen Peroxide

The goal of the study was to evaluate the effect of direct contact ofNaOH/H₂O₂ aqueous solution on hCoV-OC43, over different exposure times.

Pre-Test Preparations

Biological samples: A549 cells (Colon; ATCC, Cat. #CCL-185) were grownin 96-well plates (96-well plate, Greiner Bio One) in F-12K growthmedium (ATCC, Cat. #30-2004) supplemented with 2 mM L-Alanyl-L-Glutaminesolution (200 mM; Biological Industries, Cat. #03-022-1B), 1%Penicillin-Streptomycin solution (Biological Industries, Cat.#03-031-1B) and 10% Fetal Bovine Serum (FBS; Biological Industries, Cat.#04-127-1A), at 37° C. and 5% CO₂.

Chemical samples: 300 μl of H₂O₂ 10% solution were added to 9 ml of NaOH30% solution, to form 9.3 ml samples of the active reagent.

Experimental Protocol

Test A: Negative Control—Cytotoxic Effect of NaOH/H₂O₂ Solution

Two experiments were conducted to determine the cytotoxicity of theNaOH/H₂O₂ solution.

In experiment 1-310 μl sterile growth medium were added to 9.3 ml of theNaOH/H₂O₂ solution and incubated for 60 seconds, followed by preparationof 10-fold serial dilutions (1:10, 1:100, 1:1000, 1:10000, 1:100000 and1:1000000), and adding 150 μl/well from each dilution to the cells in 4replicate wells.

In experiment 2-500 μl sterile growth medium were added to 500 μl of theNaOH/H₂O₂ solution, and incubated for 10 seconds, followed bypreparation of 10-fold serial dilutions (1:10, 1:100, 1:1000, 1:10000,1:100000 and 1:1000000) and adding 150 μl/well from each dilution to thecells in 4 replicate wells.

Test B—Antiviral Effect of NaOH/H₂O₂ Solution

Two experiments were conducted to assess the antiviral effect of the ofthe NaOH/H₂O₂ solution.

In experiment 1—310 μl of stock hCoV-OC43 were added to 9.3 ml of theNaOH/H₂O₂ solution, and incubated for 13, 30 and 60 seconds (total 3test samples), followed by preparation of 10-fold serial dilutions(1:10, 1:100, 1:1000, 1:10000, 1:100000 and 1:1000000) and adding 150μl/well from all dilutions produced at each incubation duration, to thecells in 4 replicate wells.

In experiment 2—500 μl of stock hCoV-OC43 were added to 500 μl of theNaOH/H₂O₂ solution and incubated for 2, 5 and 10 seconds (total 3 testsamples), followed by preparation of 10-fold serial dilutions (1:1000,1:10000, 1:100000 and 1:1000000) and adding 150 μl/well from alldilutions produced at each incubation duration, to the cells in 4replicate wells.

Viral Standard Curve Preparation for Stock Titration:

Untreated hCoV-OC43 stock was diluted in 10-fold serial dilutions insterile growth medium supplemented with 2% FBS, and 150 μl/well wereapplied from each dilution to the cells in 4 replicate wells.

Four (4) additional wells were used as calibration curve negativecontrol (cNC), in which sterile medium containing no hCoV-OC43 wasapplied onto the cells.

The A549 96-well plate was incubated for 6 days at 35° C. and 5% CO2,and cells were daily monitored for cytopathic and/or cytotoxic effectsunder the microscope.

Results

Viral Standard Curve

Viable and uninfected/contaminated cells were observed in all cNC wellsin both experiment 1 and 2.

In experiment 1 standard curve titration calculated using the Reed andMuch titration formula was: 2.11·10⁶ TCID₅₀/ml.

In experiment 2 standard curve titration calculated using the Reed andMuch titration formula was: 3.09·10⁷ TCID₅₀/ml.

The results indicate that the virus stock used in each experiment standsin the calibration range of our viral stocks and is reliable forexperimentation.

Test A: Negative Control—Cytotoxic Effect of NaOH/H₂O₂ Solution

Cytotoxicity leading to cell death within hours was observed in bothexperiments for all replicates of dilutions 1:10 and 1:100. At dilution1:1,000 and above, no cell death, and no difference in cell appearancewere observed, compared to untreated cells incubated in growth mediumand no chemical treatment.

The antiviral experiment was conducted accordingly, referring to the1:1,000 viral dilution as a baseline for CPE monitoring and TCID₅₀calculations.

Test B—Antiviral Effect of NaOH/H₂O₂ Solution

No cytotoxic effect was observed for dilutions of 1:1,000 and above ofthe NaOH/H₂O₂ solution, no viral infection was observed for all testsamples in all wells infected by treated virus containing thesedilutions. That is, hCoV-OC43 infectivity by at least ≥99.9%, already at2 seconds of contact with the virus. These percentages can beinterpreted based on Table 5, for the calculated −3.7 viral logreduction obtained as the result for the 3 Test samples (Table 4).

Since no TCID₅₀ could be calculated in any of the 3 test sample wells,calculation of the viral log reduction was based on the delta betweenthe calculated TCID₅₀ units that were inoculated (following incubationwith the chemical mixture) into each well of the 1:1,000 dilutions, andthe end-point viral titer obtained (0). The TCID₅₀ inoculated into thewells was calculated based on the standard curve samples.

TABLE 3 antiviral activity experiment 1 Initial viral Observed viralViral log % Virus Samp1e TCID₅₀/well TCID₅₀ day 5 reduction reductionTEST 13 s 1.02E+01 0 1 ≥90 TEST 30 s 0 1 ≥90 TEST 60 s 0 1 ≥90

TABLE 4 Chemical mixture antiviral activity experiment 1 Initial viralObserved viral Viral log % Virus Sample TCID₅₀/well TCID₅₀ day 7reduction reduction TEST 2 s 4.64E+03 0 3.7 ≥99.9 TEST 5 s 0 3.7 ≥99.9TEST 10 s 0 3.7 ≥99.9

Legend for Table 3 and 4:

Initial viral TCID₅₀/well: the total amount of hCoV-OC43 inoculated intothe 96-well plate and onto the cells, at dilution 1:1,000 of thechemical mixture following incubation for 13, 30 and 60 seconds (Table3), and 2, 5 and 10 seconds (Table 4) of the virus in the aqueousNaOH/H₂O₂ solution. This value was calculated based on the titration ofthe viral standard curve wells, using the Reed and Much titrationformula, and normalization to the total volume inoculated into the wellsfollowing the dilution (150 μl). The initial viral TCID₅₀/well was onlycalculated for the 1:1,000 sample dilutions, as up to 1:100 there wasmassive cell death not allowing for CPE (cytopathic effect) observation.

Observed viral TCID₅₀: the TCID₅₀ obtained for each sample at theexperiment end-point (5 and 7 days post viral inoculations). As no CPEand infection were visible, all samples were assigned 0 TCID₅₀.

Viral log reduction: was calculated per the 1:1,000 sample dilutions aslog₁₀ from the initial viral TCID₅₀ per well).

TABLE 5 Interpretation of results Log reduction Percent (%) reduction ≥1≥90 ≥2 ≥99 ≥3 ≥99.9

CONCLUSION

In this study, a chemical mixture of 9 ml NaOH solution and 300 μl H₂O₂solution was tested for its ability to hamper the infectivity ofhCoV-OC43 by direct contact of the solution and virus. Results of thethree tests performed, for three different contact durations, indicatethat the tested NaOH/H₂O₂ solution abolished virus infectivity as soonas 2 seconds following the direct exposure. Since there was cytotoxiceffect of the NaOH/H₂O₂ solution to the cells at up to 1:100 dilution,in these wells CPE observations were not possible. As to 1:1,000dilution and above, we can conclude that the NaOH/H₂O₂ solution indeedreduced ≥99.9% the viral load capable of infecting the cells, comparedto the load first introduced into the wells of this dilution followingincubation in the mixture. This reduction can be assessed as at least−3.7 log reduction in hCoV-OC43 virus infectivity.

Example 6 Treatment of Low Concentration CO₂-Bearing Air by Absorptionto Aqueous Solution of Potassium Hydroxide and Hydrogen Peroxide

The goal of the study was to examine the performance of two types ofperforated membranes which differ from one another in the geometry oftheir holes. In one membrane, the diameter of the holes does not varyacross the membrane thickness, i.e., the air flows through passageswhich are cylindrically in shape, with constant diameter of 600 μm. Theother membrane that was tested was perforated with holes with uniquegeometry, as the air flows through passages consisting of a cylindricalsection joining an inverted frustoconical section: to move across themembrane, the air flows through the cylindrical section, with diameterof 300 μm, then through the frustoconical section, whose small base iscontiguous with the cylindrical section (they are equal in diameter).The large base of the frustoconical section, with diameter of 900 μm, isthe opening of the hole in the side of the membrane facing the bulksolution.

The experimental set-up was similar to the one described in Example 2,but was larger in scale. Also, this time potassium hydroxide solution50% was used. 1.1 L of the KOH solution was charged to a tubular reactorwith diameter of 26.5 cm. The membrane tested was installed 2.5 cm fromthe bottom of the tubular reactor. H₂O₂ solution (10%) was added at aflow rate of 10 ml/hour over the test period, by intermittentlyoperating the pump delivering the H₂O₂ solution. CO₂ feed and its mixwith an air stream to create a combined stream of 1200 ppm-CO₂ bearingair were carried out as described in Example 2; this stream was fed at aflow rate of 120 L/min to the reactor, where the KOH/H₂O₂ reagent washeld.

CO₂ levels in the incoming and outgoing streams were recordedperiodically over one hour by the arrangement described in Example 2,and conversion rates were calculated. The results are shown in the formof a bar diagram in FIG. 19 , illustrative of the test period. Goodconversion percentages (˜80%; right bar) were measured for the membranedperforated with 600 μm holes. As to the geometrically-modifiedperforated membrane, it is seen that almost 100- conversion percentageof CO₂ was maintained over the one-hour test period (left bar).

1) A method for improving indoor air quality in a room, comprisingdrawing air from the room and guiding the air into a gas/liquidcontactor charged with aqueous alkali hydroxide/H₂O₂ solution, passingthe air through a perforated membrane installed in the gas/liquidcontactor below the surface level of the aqueous alkali hydroxide/H₂O₂solution, such that bubbles produced travel through said solution, andgetting treated air with improved quality from said gas/liquidcontactor, said treated air is characterized by having: reduced carbondioxide levels; and/or reduced VOC levels; and/or reducedmicrobiological load. 2) The method according to claim 1, wherein theair is passed through the membrane via perforations whose diameterincreases across the membrane thickness. 3) The method according toclaim 2, wherein each of the perforations is a passage consisting of acylindrical section joining an inverted frustoconical section facing thesolution, or a passage shaped as a frustrum of a cone with its largebase facing the solution. 4) The method according to claim 1, whereinthe aqueous alkali hydroxide/H₂O₂ solution is charged to the gas/liquidcontactor either by feeding alkali hydroxide solution preparedbeforehand or by dissolving solid alkali hydroxide in water suppliedseparately to the gas/liquid contactor, with continuous or periodicaddition of hydrogen peroxide solution to the alkali hydroxide solution.5) The method according to claim 4, comprising periodic dissolution ofsolid alkali hydroxide in a tablet form to water supplied separately tothe gas/liquid contactor. 6) The method according to claim 1, whereinthe concentration of the alkali hydroxide solution is from 5 to 48%-50%by weight, the concentration of the hydrogen peroxide solution added isfrom 3 to 35% by weight, with volumetric ratio between the solutions inthe range of 2:1 to 10:1 in favour of the alkali hydroxide solution,wherein the ratio is adjusted based on the CO₂ level and/or microbialload. 7) The method according to claim 1, comprising: drawing indoor airand passing same, at a first flow rate, across a filter to captureairborne particles and produce a main filtered air stream; diverting aportion of the main filtered air stream to generate a secondary filteredair stream flowing at a second flow rate; forcing said secondaryfiltered air stream into a gas/liquid contactor charged with the aqueousalkali hydroxide/H₂O₂ solution, where the filtered air, in the form ofbubbles, is contacted with said solution; withdrawing filtered anddecontaminated air stream from said gas/liquid contactor; and joiningsaid filtered and decontaminated air stream with the main filtered airstream. 8) The method according to claim 1, wherein CO₂ level in indoorenvironment is reduced from 1000-10,000 ppm down to than 400-700 ppm. 9)The method according to claim 1, wherein VOC level in indoor environmentis reduced. 10) The method according to claim 9, wherein the VOC isformaldehyde. 11) The method according to claim 1, wherein bacterialload and/or viral load in indoor environment is reduced by at least 2log reduction. 12) An air purifier for eliminating chemical andbiological pollutants from a room, comprising: an inlet air channel; oneor more air sucking components configured to direct air from the roominto said inlet channel, and to direct the air via said air channel intoa perforated membrane mounted in a chemical and biologicalpollutants-elimination reactor; and an outlet air channel configured toreceive treated air from the reactor; wherein the reactor comprises: areservoir configured to contain a purifying aqueous alkalihydroxide/H₂O₂ solution; wherein during the purifier's operation, saidperforated membrane is positioned below a surface level of the solutionsuch that air passing through the perforated membrane is converted intobubbles that travel through the solution and towards said outletchannel; and wherein the air purifier further comprises a removablestorage unit positioned above the reactor, said removable storage unitis configured to contain and supply alkali hydroxide, hydrogen peroxide,and optionally water to said reactor. 13) The air purifier according toclaim 12, wherein said inlet air channel conveys air in a downwardsdirection, the inlet air channel passes through an opening in saidperforated membrane towards an air compartment located below theperforated membrane. 14) The air purifier according to claim 12, whereina bottom outlet of said inlet air channel is sealed against a topsurface of the perforated membrane, thereby to allow passage of air fromthe inlet air channel only through the perforations of the membranetowards a section of the reservoir below the membrane, and wherein thediameter of said membrane is smaller than the diameter of said reservoirof alkali hydroxide/H₂O₂ solution. 15) The air purifier according toclaim 12, wherein each perforation at the membrane has a diameter in therange of between 40 μm and 1200 μm. 16) The air purifier according toclaim 12, characterized in that the perforated membrane has perforationswith top and bottom openings, respectively, at top and bottom surfacesof the perforated membrane, the diameter of said top opening is largerthan a diameter of said bottom opening. 17) The air purifier accordingto claim 16, wherein each of the perforations is divided into twosections in cross-section, a lower section having a cylindrical shape,and an upper section having a frustoconical shape. 18) The air purifieraccording to claim 12, wherein a bottom outlet of said inlet air channelis configured to lead contaminated air to a perforated membrane, saidperforated membrane having a spiral tubing configuration and positionedat a lower portion of said purifying solution's reservoir. 19) The airpurifier according to claim 18, wherein each said perforations ispositioned at a lower portion of the tubing in cross section, therebydirecting air outlet through the perforation downwards. 20) The airpurifier according to claim 19, wherein each of said perforations ispositioned at least 30° lower than the tubing horizontal diameter incross-section. 21) The air purifier according to claim 18, wherein eachof said perforations has a diameter in the range of between 40 μm and1200 μm. 22) The air purifier according to claim 18, wherein a distancebetween each two perforations is in the range of 2-50 of theperforation's diameter. 23) The air purifier according to claim 12,wherein said storage unit comprises an alkali hydroxide container, aH₂O₂ container, and optionally a water container. 24) The air purifieraccording to claim 23, having an essentially cylindrical shape, whereinsaid alkali hydroxide container, said H₂O₂ container, and said watercontainer are arranged concentrically within the storage unit. 25) Theair purifier according to claim 23, wherein the alkali hydroxidecontainer is configured to contain alkali hydroxide tablets in areleasable arrangement. 26) The air purifier according to claim 25,wherein said alkali hydroxide container comprises a plurality ofcolumns, each column is configured to store alkali hydroxide tablets.27) The air purifier according to claim 26, wherein said hydroxidecontainer is configured to angularly revolve, thereby to position asingle column above an opening to a passage leading to said solutionreservoir, thereby to allow a periodical feeding of the solution byhydroxide tablets. 28) The air purifier according to claim 12, furthercomprising a blower and a HEPA filter fitted in the inlet channelupstream to the reactor. 29) The air purifier according to claim 12which is integrated with a domestic room purifier having a HEPA filter,wherein the inlet air channel is a branch from an inlet air channel ofthe domestic room purifier diverging downstream to the HEPA filter, andwherein the outlet channel joins an outlet channel of the domestic roompurifier. 30) The air purifier according to claim 12, further comprisinga sensor for measuring a concentration of CO₂ at the room-air, andwherein a schedule and a period of operation of the device is based onCO₂ measurements by said sensor. 31) A home air purifying system,comprising: a plurality of air-quality sensors, each sensor beingpositioned at another room of the home; a docking station which isconfigured to: host a mobile, air purifier; receive air qualitymeasurements from all said plurality of sensors, and determine when alevel of contamination at a room exceeds a predefined contaminationthreshold; and communicate with said mobile air purifier, and at leastsend to it an indication of a room in which a contamination above saidpredefined contamination threshold has been detected; and said mobileair purifier, which is configured to: communicate with said dockingstation, and at least receive from it an indication of the room in whichthe contamination above said predefined contamination threshold has beendetected; upon receipt of said indication, navigate to the contaminatedroom, operate there to purify the room, and upon completion, return tothe docking station. 32) The system according to claim 31, wherein saidcontamination comprises one or more chemical and biologicalcontaminants. 33) The system according to claim 31, wherein said mobileair purifier comprises: an inlet air channel; one or more air suckingcomponents configured to suck air from the room into said inlet channel,and to direct the air via said air channel into a perforated membranemounted at a bio-hazards elimination reactor; and an outlet air channelconfigured to receive treated air from the reactor, and to return thetreated air into the room; wherein the bio-hazards elimination reactorcomprising: a reservoir configured to contain a purifying aqueous alkalihydroxide/H₂O₂ solution; wherein during the purifier operation saidperforated membrane is positioned below a surface level of the solutionsuch that air passing through the perforated membrane is converted intobubbles that travel through the solution and towards said outletchannel; and wherein the air purifier further comprising a removablestorage unit positioned above the reactor, said removable storage unitis configured to contain and supply alkali hydroxide, hydrogen peroxide,and water to said reactor. 34) A method of improving indoor air quality,comprising: providing airflow through CO₂ adsorption scrubber over afirst period of time to capture CO₂ by an adsorbent in the scrubberwhile reintroducing CO₂-depleted air from the scrubber into a room;desorbing CO₂ from the adsorbent during a second period of time whileguiding air laden with the desorbed CO₂ from the scrubber into agas/liquid contactor charged with aqueous alkali hydroxide/H₂O₂solution, passing the CO₂-laden air through a perforated membraneinstalled in the gas/liquid contactor below the surface level of theaqueous alkali hydroxide/H₂O₂ solution, such that bubbles producedtravel through said solution, and getting treated air with reduced CO₂level from said gas/liquid contactor. 35) An air purifier comprising: adevice used to move air for supplying air flow through the air purifier;CO₂ adsorption scrubber; a gas/liquid contactor located downstream ofthe scrubber; an outlet pipe to release air from the air purifier to theroom; a first air flow line connecting said device to the outlet pipe,configured to direct incoming air stream to the adsorption scrubber, andoutgoing air stream from the scrubber to said outlet pipe; a second airflow line connecting said device to the outlet pipe, configured todirect incoming air stream to the gas/liquid contactor, and outgoing airstream from the gas/liquid contactor to the outlet pipe; and a third airflow line connecting said device to the outlet pipe, configured todirect incoming air stream to the adsorption scrubber, and outgoing airstream from the scrubber to the gas/liquid contactor; an array of valvesto guide the moving air through said first, second or third air flowlines; optionally a heater positioned downstream to the adsorptionscrubber.